Fuel system purge



W. C. SPENCER ET AL FUEL SYSTEM PURGE Filed May 3l, 1966 O June 18, 1968 United States Patent O 3,388,549 FUEL SYSTEM PURGE William C. Spencer and Arthur V. Barnett, Bakersfield,

Calif., assignors to Mobil Oil Corporation, a corporation of New York Filed May 31, 1966, Ser. No. 554,035 19 Claims. (Cl. 6il-l3) ABSTRACT F THE DISCLOSURE This specification discloses a method and apparatus for purging the fuel system of a power generator upon stoppage thereof, the generator being fueled by a liquid fuel which is highly viscous and, in order that it can be used in the system, is heated by heat derived from the generator to reduce its viscosity. Upon stoppace of the power generator, a signal is generated which discontinues the supply of the liquid fuel to the generator and passes a purge liquid through the fuel system to remove the liquid fuel before the liquid fuel cools and thickens. A purge gas additionally to the purge liquid can be passed through the system in response to the signal. Further, in response to the signal, the output from the power generator can be disconnected from the means operated by the generator.

This invention relates to a method and apparatus for purging a fuel system and relates more particularly to a method and apparatus for purging the fuel system of a power generator fueled by a highly viscous liquid fuel.

Many power generators are fueled by liquid fuels which at atmospheric temperatures are highly viscous. These fuels, at atmospheric temperatures, are too viscous to flow, at the pressures ordinarily employed, through the pumps, valves, lines, injectors, jets, air mixers, burners, and the like, of the fuel system. However, at higher temperatures, with resultant decrease in viscosity because of the higher temperatures, these fuels are able to iiow with relative ease through the fuel system. Thus, in the operation of these power generators, the fuel is heated and ordinarily the most economical source of heat for heating the fuel is waste heat having its origin in the generator. On the other hand, while the waste heat is the most economical source of heat for decreasing the viscosity of the fuel, the use of the waste heat presents problems where operation of the generator ceases, particularly where the cessation of operation is unintentional as through malfunction or otherwise. In such cases, the waste heat is no longer available and the fuel within the fuel system cools down and its viscosity increases. As a result, the fuel system is filled with highly viscous liquid that will not flow within the system at the pressures designed for normal operation and, in this condition, the generator cannot be started again.

More particularly, for the operation of a turbine by a power generator comprising one or more free piston gasiers providing gas to the turbine, crude petroleum, or oil, can be employed as fuel for the gasiiiers. The crude oil, depending upon its type, will be more or less highly viscous. However, employing the heat in the exhaust gas leaving the turbine for heating the crude oil, even crude oil having the consistency almost that of a gel at atmospheric temperatures can be used. In starting the gasier, a liquid fuel of relatively low viscosity and capable of flowing through the fuel system at atmospheric temperatures and at the pressures designed for normal operation, such as diesel oil, is employed. As soon as the gasiiier is operating at equilibrium conditions and waste heat is available, crude oil is heated by the Waste heat and is substituted for the diesel oil as the fuel to the gasi- ICC fier. But, with shutdown of the generator and the heat in the exhaust gas from the turbine no longer being available, the crude oil cools and, as it approaches atmospheric temperatures, will resume its 4highly viscous state. This highly viscous oil will occupy the lines, valves, injection pump, and other parts of the gasiiier fuel system and, in order to get the generator back into operation, the highly viscous oil must be removed from the fuel system. Frequently, this will involve dismantling of the fuel system. Thus, inordinate delays can be encountered in getting the generator back into operation after there has been a stoppage.

It is an object of this invention to provide a method and apparatus for purging a fuel system.

This and other objects of the invention will become apparent from the following detailed description.

In accordance with the invention, there are provided a method and apparatus for shutting olf the supply of a heated, normally highly viscous liquid fuel to the fuel system of a power generator upon stoppage of the generator and supplying a purge liquid to the fuel system to remove therefrom the fuel before it becomes cool, and thus more viscous, to any significant extent. In a particular embodiment of the invention, there are also provided a method and apparatus for additionally purging at least a portion of the fuel system with a gas. In still another embodiment of the invention, there are provided a method and apparatus for draining liquids from the power generator. In a further embodiment of the invention, there are provided a method and apparatus for disconnecting the output from the generator from the means operated by the generator.

Broadly, the invention involves the method of and apparatus for, first, the development of a signal upon stoppage of the power generator. In response to this signal, the supply of the normally, highly viscous liquid fuel to the power generator is discontinued. Simultaneously, a purge liquid having a low viscosity at atmospheric temperatures is supplied to the fuel system for a predetermined period of time. Also simultaneously therewith, and for the same period of time, there can be supplied to at least part of the fuel system a purge gas. Further, also simultaneously therewith, the output from the power generator can be disconnected from the means operated by the generator.

rlhe single ligure is a schematic representation of a particular embodiment of the invention.

Referring now to the figure, gasiiier 6 provides gas for the operation of expander turbine 7 which in turn operates air compressor 8. The gasiier and the turbine are the prime mover for the air compressor. The compressed air produced by the air compressor can be used for any desired purpose, as for example, injection into a subterranean formation containing oil for recovery of the oil by the in-situ combustion procedure. The gasilier 6 is a free piston gasifier. Free piston gasiiiers are well known and are disclosed in Business Week, April 25, 1953, pages 101 and 102; World Oil, July 1965; and U.S. Patent No. 2,478,375. Stated generally, a free piston gasiiier utilizes a two-stroke diesel cycle to generate hot pressured gases and the hot pressured gases can be transformed into mechanical power by an expander turbine. The free piston gasier uses two horizontally opposed pistons operating in a common power cylinder within the gasier casing. The liquid fuel for the gasier is injected by means of fuel injectors into the power cylinder and upon ignition of the fuel the two horizontally opposed pistons move outwardly from each other within the power cylinder. Each of the pistons is rigidly connected with a compressor piston operating within compressor cylinders, the outboard ends of which form air cushions. The air cushions absorb the energy from the compressor pistons as they move outward. When sufcient pressure has been built up in the air cushions to stop the pistons, the air cushions begin to expand driving the compressor pistons inward for the next cycle. Movement of the pistons allows the gases produced by combustion of the fuel to leave the gasitier.

The hot pressured gases leave the gasifier and enter exhaust gas receiver 9. They then pass through exhaust control valve and through line 11 to header 12. From header 12 the gases pass through line 13 to the expander turbine 7. Header 12 can be a common header and the gases from one or more other gasiliers required for operation of the expander turbine 7 may enter the header. Line 14 is also connected to valve 10 and leads to exhaust stack 15.

The gasifier 6 can operate with crude oil as the fuel. This crude oil, as mentioned, is too viscous for ready flow at atmospheric temperature in the fuel system of the gasier at the pressures normally and desirably employed in the system and is heated to reduce its viscosity prior to entering the fuel system. The crude oil is pumped from crude oil storage tank 16 through line 17 by means of pump 18 contained in the line 17 to heat exchanger 21. Pumping of the oil from the storage tank at atmospheric temperatures to the heat exchanger ordinarily presents no problem since the lines can be designed to sufficient size to operate at moderate pressures to effect flow of the oil. In heat exchanger 21, the crude oil is placed in indirect heat exchange with heating oil entering the heat exchanger through line 22. The heating oil leaves the heat exchanger through line 23 and returns to heat exchanger 24 where it is placed in indirect heat exchange with hot exhaust gas entering through line 25 from expander turbine 7. The hot exhaust gas leaves heat exchanger 24 through line 26.

The heated crude oil then leaves the heat exchanger 21 through line 27 and passes to valve 28. From valve 28 the heated crude oil passes through line 31 to fuel injection pump 32 and is pumped by the pump through line 33 to fuel injector 34. The heated crude oil then enters the power cylinder through the injector. The pump 32 is capable of supplying more fuel to the injector 34 than is required for operation of the gasier and this excess of fuel passes from the injector through line 35 to a storage tank. For purposes of simplicity of illustration, only one injector 34 is shown. However, it will be understood that more than one injector can be employed. For example, three injectors may be employed.

Upon stoppage of the gasier 6, which may be an unintentional or an intentional stoppage, supply of the heated crude oil to the gasitier is discontinued and simultaneously therewith the purge liquid is passed through the fuel system. As shown, the fuel system comprises the valve 28, line 31, pump 32, line 33, injector 34, and line 35. This purge liquid is one in which the crude oil is soluble and which has a viscosity at atmospheric temperatures which is less than the viscosity of the crude oil at these same temperatures and which permits its ready ow through the fuel system at the normal pressures employed in the fuel system. Thus, this purge liquid can wash the crude oil from the fuel system and where it remains thereafter in the fuel system can readily fiow through the fuel system at atmospheric temperatures. Preferably, the purge liquid is the same liquid which is employed as the fuel for starting the gasier. Thus, diesel oil can be employed as the purge liquid.

Stoppage of the gasier operates pressure switch 40. This pressure switch is connected through line 41 to one of the air cushions of the gasitier 6. With stoppage of the gasifer, the pressure within the air cushions decreases and the switch responds to this decrease in pressure, i.e., to the signal developed, to close contacts 42. One of contacts 42 is connected to Ia source of electrical current 43 through line 44 and with closing of the contacts the current will pass through line 45 to point 46. From point 46 the current will pass through line 50, through contacts 51,

which are closed during operation of the gasitier with` crude oil as the fuel, and then through line S2 to points 53 and 54. From point 53 the current will pass through line 55 and will actuate timing 4relay 56. The timing relay 56 operates to close contacts 61 and will, upon actuation, remain in its actuated position to keep contacts 61 closed for a predetermined period of time. As will later become apparent, during the predetermined period of time that the timing relay remains in its actuated position, purge liquid is supplied through the valve 28 to the line 31, the fuel injection pump 32, the line 33, and the fuel injector 34 and the line 35. A period of supply of purge liquid of about five minutes has been found to be satisfactory. Thus, the timing relay is designed to remain in its actuated position for about five minutes and contacts 61 will remain in their closed position for this same period of about five minutes. Contacts 61 are timing contacts which time open, i.e., they close practically immediately upon operation of the timing relay and then hold for the predetermined period of time before opening. Accordingly, practically instantaneously with closure of contacts 42 upon operation of pressure switch 40, contacts 61 will have closed.

Closing of contacts 42 also permits electrical current to pass through line 62 and this current will actuate slave relay 63. As will vbe explained later, contacts 51 will open with opening of contacts 42 but this will occur after contacts 61 have already closed. Further, with closing of contacts 61, the timing relay 56 supplies current to itself from source 43 through line 64, closed contacts 65, line 70, closed contacts 61, point 54, line 52, point 53, and line 55. The current will also flow from point 54 through the line 62 to the slave relay 63. Thus, regardless of the opening of contacts 51, the slave relay will be actuated by the supply of current thereto until such time that contacts 61 are opened by the timing relay 56 ceasing operation at the end of the predetermined period of time, i.e., about tive minutes;

With activation of slave relay 63, contacts 72, 73, and 74 will close simultaneously. Upon closing of contacts 72, current from line 75 will pass through line 80 to point 81. From point 81, the current Will pass through line 82 and activate relay 83 which closes contacts 84 and S5. Contacts 84 being closed, current from source 43 passing through line 64, contacts 65, and line passes through the contacts 84 to line 91 and actuates solenoid motor valve operator 92 which operates air valve 93. Air under pressure enters air valve 93 through line 94 and the pressure of this air is imposed through line upon pneumatic motor valve operator 101. With operation of the air Valve 93, the air passing through the valve is blocked and the pressure imposed upon the pneumatic motor valve operator 101 through line .100 is vented to the atmosphere through line 102. Upon relief of this pressure, pneumatic motor valve operator 101 closes threeway valve 28 to the flow of heated crude oil from the line 27 through the line 31 to the fuel injection pump and from the pump to the fuel injector 34. Thus, with stoppage of the gasier 6, the ow of crude oil to the gasier ceases.

Simultaneously with the stopping of the heated crude oil to the fuel system, the purge liquid, as indicated, consisting of diesel oil is passed into the fuel system. With closing of contacts 73, the current from line 75 passes through line 102 to relay 103 and the relay closes contacts 104. Contacts 104 closing, current from source 43 passing through line 64 to point 105 and from point 105 through line 106 will pass through line 110 to starter 111. The current going to starter 111 actuates the starter to send current from source 112 through line 113 to pump 114 to operate the pump 114. This pump is connected through line 115 to storage tank 120 and with operation of the pump 114 the diesel oil passes through line 121 the heated crude oil through the line 27 is at the same time opened to the tlow of the diesel oil. Thus, the diesel oil passes through the line 31, the pump 32, the line 33 to the fuel injector Iand the line 35 and washes these lines, the pump, and the fuel injector free of the crude oil before the crude oil has time to cool and become highly viscous. i

As just described, simultaneously with the discontinuance of the supply of heated crude oil to the fuel system, the diesel oil is supplied to the system. In addition thereto, there is simultaneously supplied to the line 35 a supply of air to assist in purging the line 35 o the crude oil and removing diesel oil. Upon closing of contacts 74 of the slave relay 63, the current from line 75 ows through line 122 to actu-ate solenoid motor valve operator 123 which operates air valve 124. The air valve is provided with air under pressure entering from line 125 and operation of air valve 124 imposes the pressure of this air through line 131i which operates pneumatic motor valve operator 131 to open valve 133. With opening of this valve, air under pressure from line 134 enters line 135 and passes to the line 35 from the fuel injector 34.

As mentioned, the header 12 is a common header and gas from one or more other gasiers can be supplied to it. In this situation, with the gasier 6 no longer operating, the gas from another gasier being supplied to the header could flow into gasier 6 with possible damage to this gasiter. This is prevented by closing valve 1t) to the backward flow of gas through line 11. With operation of pressure switch 40 and closing of contacts 42, current, as previously described, tlows from source 43 to point 46. This current will then ow through line to, and actuate, solenoid motor valve operator 141. Actuation from a source (not shown) of the operator 141 operates a pilot (not shown) to release hydraulic pressure on valve 10 which permits the valve to close. With closure of valve 10, line 11 is closed and line 14 is opened to the exhaust stack 15. The exhaust gas receiver 9 is thus opened to the atmosphere.

During operation of the gasier 6, lubricant can accumulate to some extent in the casing of the gasier. Excessive accumulation of liquids is undesirable and these liquids are drained from the gasier case. Accumulation of liquid occurs at a fairly steady rate during normal operation of the gasitier and periodic draniage under these conditions is satisfactory.

Periodic drainage of the gasiiier case is controlled by timer 142. This timer operates cam 143 and is designed to make one revolution of the cam in any given period of time. For example, the timer may be designed to make one revolution of the cam each hour. Revolution of the cam operates to close switch 144 and switch 144 can be spring-loaded or otherwise constructed to be in its open position except when closed by cam 143. Further, the cam 143 is designed to keep switch 144 closed for a predetermined period of time which may be, for example, about one minute. Thus, operation of timer 142 closes switch 144 for a predetermined time within successive predetermined periods which, for the examples given, would be one minute every hour.

Closing of switch 144 permits electrical current to ow from source 145 through line 150 to timing relay 151 and from the timing relay through line 152 and line 153, thus actuating the timing relay 151. Actuation of the timing relay 151 closes contacts 154 for a predetermined period of time less than the one minute that switch 144 is closed. For example, this period of time can be tive seconds. This permits electrical current from source 145 to ow for live seconds through line 155 to solenoid motor valve operator 159 and from this valve through line 160, contacts 154, line 153, and the switch 144. This ow of current actuates the operator 159 which operates air valve 161. The air valve 161 is provided Iwith air under pressure from line 162 and the pressure of this air is imposed through line 163 upon pneumatic motor valve operators 164 and 165. Operation of air valve 161 vents the pressure from line 163 to atmosphere through line 166 and release of the pressure actuates the operators k164 and 165. Drain line 170 leads from one end of the casing of the gasiiier and is joined by drain line 171 leading from the other end of the casing of the gasitier. Drain line 170 is provided 'with valve 173 which is operated by pneumatic motor valve operator 164. Actuation of operator 164 opens valve 173 permitting drainage of the liquid accumulated at the ends of the gasier case. Drain line 174 leads from the center portion of the casing of the gasi'ier and is provided with valve 175 which is operated by pneumatic motor valve operator 165. Actuation of operator 165 opens valve 175 permitting drainage of liquid accumulated at the center portion of the casing of'the gasifier. The valves 173 and 175 will remain open and drainage will occur until switch 154 of timing relay 151 opens following the predetermined time itis actuated by switch 144 operating off cam 143. Thus, the casing of the gasier is drained, for the examples given, for tive seconds every hour.

As stated previously, timing relay 55 closes contacts 61 which in turn actuates slave relay 63 closing simulta neously contacts 72, 73, and 74. With the simultaneous closing of these contacts, the supply of crude oil to the fuel system is discontinued, diesel oil is pumped through the fuel system to purge it of the crude oil, air is passed through the line 35 leading from the fuel injector and the exhaust gas receiver 9 of the gasier is connected to the exhaust stack. Discontinuance of the supply of crude oil to the fuel system and connection of the exhaust gas receiver to the exhaust stack may be maintained until the gasier is started again.l However, the supply of purging liquid to the fuel system and the air to the line from the injector need be continued only until the crude eil is purged from the fuel system. Supply of the purging liquid and the air for a predetermined period of time required to purge the fuel system of the crude oil is controlled by the timing relay 56. This relay is designed to naintain contacts 61 in its closed position for this predetermined period of time. On the other hand, it is desired that the timing relay be actuated only once for any one stoppage of the gasiier. Thus, it is desired that the timing relay shut itself ot, i.e., time itself out, and not be actuated again until the next stoppage of the gasitier.

With contacts 72 being closed, as previously described, the pressure on pneumatic motor valve operator 101 is released to operate valve 23. However, with the release ot pressure on the operator 101, the pressure is also released on pressure switch connected by line 131 to the operator 101. Pressure switch 180, on release of the pressure, opens contacts 51 whereby the current flowing to timing relay 56 through line 52 to point 53 and then through line 55 is cut ott. Thus, the timing relay no longer runs on this current. However, -with closing of the contacts 61, current flowing from the source 43 through line 64, contacts e5, and line 70 passes through line 71, closed contacts 61, points 54 and 53 and line 55 t0 the timing relay, thus keeping this relay in operation. After the timing relay 56 has operated for its predetermined period of time, it opens contacts 61 thereby cutting off the current to itself. Further, with contacts 51 being open, no other current flows to the timing relay and the timing relay thus operates only once and for the predetermined period of time for one stoppage of the gasier.

With opening of contacts 61 after the timing relay 55 has operated for its predetermined period of time, the slave relay 63 ceases operation and contacts 72, 73, and 74 open. With this, the diesel oil pump 114 ceases operation and the air to the line from the fuel injector is discontinued. However, contacts 42 remain closed and current will still be supplied to solenoid motor valve operator 141 to maintain valve 10 in its position connecting the exhaust gas receiver 9 to the exhaust stack 15. Furthermore, valve 28 remains in its position closing off the supply of crude oil to the fuel injection pump. With closing of contacts 84 and 85 by relay 83 actuating valve 28, the current continues to flow to the relay from source 43, line 64, contacts 65, line 90, contacts 85, line E83, and the contacts S4. Thus, contacts S4 and 85 will remain in their closed position until the supply of current to the relay 83 is cut olf.

Supply of current to the relay 83 is cut off to open contacts 84 and 85 by operation of manual switch 184. Operation of this latter switch opens contacts 65 and closes contacts 185. Opening of contacts 65 discontinues the supply of current through line 90 to line 183, thus discontinuing operation of the relay 83. However, closing of contacts 185 supplies current to solenoid motor valve operator 92 from line 64 through line 1M) to line 91. Thus, the solenoid motor valve operator remains in its previous position to maintain the valve 28 in its position closing off the supply of crude oil to the fuel injection pump 32. However, since, as previously stated, the gasier 6 is operated initially with diesel fuel until such time that waste heat from the expander turbine is available for heating the crude oil, the svalve 28 is in position .for starting of gasilier 6. Additionally, the relays, valves, timers, switches, and other elements of the apparatus described are in position to effect purging of the fuel system in the event of a stoppage of the gasifier after it has been started again.

The invention has been described particularly in connection with a free piston gasifier and operating an expander turbine which, in turn, operates an air compressor. However, the invention is equally applicable to any type of power generator operating on a liquid fuel which is excessively viscous at atmospheric temperature and will not flow through the fuel system of the generator without being heated, particularly where the heat for the fuel is derived from the power generator, Further, the power generator may be employed to operate other equipment than an expander turbine and the expander turbine operate other equipment than an air compressor.

Having thus described our invention, it lwill be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

We claim:

1. A method for purging the fuel system of a power generator upon stoppage of said power generator, said power generator being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said power generator is heated to reduce its viscosity by heat having its origin in said power generator, comprising developing a signal upon stoppage of said power generator, and, in response to said signal, discontinuing supply to said fuel system of said liquid fuel and supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature, and, also in response to said signal, supplying a purge gas to at least a portion of said fuel system in addition to said purge liquid.

2. A method for purging the fuel system of a power generator upon stoppage of said power generator, said power generator being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said power generator is heated to reduce its viscosity by heat having its origin in said power generator and said power generator providing a heated gas under pressure through an exhaust system to an expander turbine, comprising developing a signal upon stoppage of said power generator, and, in response to said signal, discontinuing supply to said fuel system of said liquid fuel and supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature, and, also in response to said signal, venting said exhaust gas system to the atmosphere.

3. An apparatus for purging the fuel system of a power generator upon stoppage of said power generator, said power generator being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said power generator `is heated to reduce its viscosity by heat having its origin in said power generator, comprising means for developing a signal upon stoppage of said power generator, means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel, means responsive to said signal for supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature, and means responsive to said signal for supplying a purge gas to at least a portion of said fuel system in addition to said purge liquid.

4. An apparatus for purging the fuel system of a power generator upon stoppage of said power generator, said power generator being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said power generator is heated to reduce its viscosity by heat having its origin in said power generator, comprising means for developing a signal upon stoppage of said power generator, means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel, and means responsive to said signal for supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature,

(a) said means responsive to said signal including a pneumatic switch, and

(b) said means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel and said means responsive to said signal for supplying to said fuel system said purge liquid including (l) a timing relay actuated by said pneumatic switch and operating for a predetermined period of time and (2) a plurality of electrical contact means actuated by said timing relay,

one of said electrical contact means upon actuation thereof etfecting operation of said means for discontinuing said supply to said fuel system of said liquid fuel and another of said electrical contact means upon actuation thereof effecting operation, for said predetermined period of time said timing relay operates, of said means for supplying to said fuel system said purge liquid.

5. An apparatus for purging the fuel system of a free piston gasilier upon stoppage of said free piston gasier, said free piston gasier supplying heated gas under pressure to an expander turbine through an exhaust gas system and being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said free piston gasitier is heated to reduce its viscosity by heat having its origin in said free piston gasilier, comprising means for developing a signal upon stoppage of said free piston gasier, means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel, and means responsive to said signal for supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature, said means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel and said means responsive to said signal for supplying to said fuel system said purge liquid including (a) a pneumatic switch responsive to a decrease in pressure in said free piston gasiiier upon stoppage thereof,

(b) a timing relay supplied by electrical current by operation of said pneumatic switch and operating for a predetermined period of time a slave relay,

(c) a plurality of electrical contact means operated by said slave relay,

one of said electrical contact means actuating relay means which actuates air valve means (l) to discontinue said supply of said liquid fuel to said fuel system,

(2) to operate electrical contact means to discontinue said electrical current to said timing relay supplied by operation of said pneumatic switch, and

(3) to vent said exhaust gas system to the atmosphere, and

(d) means for providing a supply of electrical current to said timing relay for said predetermined period of time said timing relay will operate,

another of said electrical contact means connected through relay means to provide electrical current to a pump for pumping a purge liquid to said fuel system for said predetermined period of time said timing relay will operate, and another of said electrical contact means operating air valve means to provide a purge gas to at least a portion of said fuel system for said predetermined period of time said timing relay will operate.

6. The method of claim 2 in which said signal is a pneumatic signal.

7. The method of claim 2 wherein said liquid fuel is crude oil and said purge liquid is diesel oil.

8. An apparatus for purging the fuel system of a power generator upon stoppage of said power generator, said power generator being fueled by a liquid fuel which is highly viscous at atmospheric temperatures and which for use in said power generator is heated to reduce its viscosity by heat having its origin in said power generator, said power generator providing a heated gas under pressure through an exhaust gas system to an expander turbine, comprising means for developing a signal upon stoppage of said power generator, means responsive to said signal for discontinuing supply to said fuel system of said liquid fuel, means responsive to said signal for supplying to said fuel system a purge liquid to remove said liquid fuel from said fuel system before said liquid fuel attains atmospheric temperature, and means responsive to said signal for venting said exhaust gas system to the atmosphere.

9. The apparatus of claim 8 wherein said means for developing said signal is means for developing a pneumatic signal.

10. The method of claim 1 in which said signal is a pneumatic signal.

t1. The method of claim 1 wherein said liquid fuel is crude oil and said purge liquid is diesel oil.

12. The apparatus of claim 3 wherein said power generator provides a heated gas under pressure through an exhaust gas system to an expander turbine and including, in addition, means responsive to said signal for venting said exhaust gas system to the atmosphere.

i3. The apparatus of claim 3 wherein said means for developing said signal is means for developing a pneumatic signal.

14. The apparatus of claim 4 wherein said power generator is a free piston gasirier.

l5. The apparatus of claim i4 wherein said pneumatic switch is responsive to decrease in gas pressure within said free piston gasitier upon stoppage thereof and said timing relay operates a slave relay which in turn actuates said plurality of electrical contact means for the period of time said timing relay operates.

16. The apparatus of claim 15 wherein one of said electrical contact means effects operation of pumping means for supplying said purge liquid to said fuel system.

i7. The apparatus of claim 15 wherein one of said electrical contact means effects operation of means for supplying a purge gas to at least a part of said fuel system in addition to said purge liquid.

18. The apparatus of claim i5 wherein one of said electrical Contact means effects operation of means for venting the exhaust gas system of said free piston gasilier to the atmosphere.

19. The apparatus of claim 5 including means for periodically draining liquid from said free piston gasiier.

References Cited UNTED STATES PATENTS 2,768,496 10/1956 Stamm 123-127 2,940,435 6/1960 Nemec 123-139 3,022,425 2/1962 Rockstead 12S- 127 3,310,097 3/1967 Fleischer 123-139 MARTN P. SCHWADRON, Primary Examinez'.

MARK M. NEWMAN, Examiner.

D. HART, Assistant Examiner. 

